package interview;

public class interview_08_01 {
    public int waysToStep(int n) {
        long[] dp=new long[n+1];
        if(n==1) return 1;
        if(n==2) return 2;
        if(n==3) return 4;
        dp[0]=1;
        dp[1]=1;
        dp[2]=2;
        dp[3]=4;
        for(int i=4;i<n+1;++i){
            dp[i]=dp[i-1]+dp[i-2]+dp[i-3];
            dp[i]%=1000000007;
        }
        return (int) dp[n];
    }
}
